Phenylbutyric acid suppresses protein accumulation-mediated ER stress in retrovirus-infected astrocytes and delays onset of paralysis in infected mice

Zinc-dependent changes in oxidative and endoplasmic reticulum stress during cardiomyocyte hypoxia/reoxygenation

Myocardial zinc dyshomeostasis is associated with caspase-3 activation, ErbB2 degradation and apoptosis during hypoxia/reoxygenation. Zinc pyrithione replenishes intracellular zinc, suppresses caspase-3, augments ErbB2 levels and improves cell survival. We hypothesize that zinc is capable of modulating redox and endoplasmic reticulum (ER) stress in the setting of cardiomyocyte hypoxia-reoxygenation. Hypoxia/reoxygenation lowered intracellular zinc, increased ER as well as oxidative stress in H9c2 cells, both of which were effectively attenuated by zinc supplementation. Silencing of gp91phox attenuated oxidative and ER stress, decreased caspase-3 activation and improved cell survival. Mimicking the oxidative insult using 50 μM H2O2 increased the caspase-3 activity that correlated with decreased ErbB2 levels, concomitant with augmented ER stress. N-acetyl cysteine (NAC) administration completely suppressed ER stress as well as caspase-3 activity. Zinc depletion using TPEN also resulted in lowered ErbB2 and increased apoptosis, along with NOX2 mRNA upregulation, increased oxidative and ER stress. Repletion with zinc suppressed NOX2 mRNA, lowered oxidative as well as ER stress and decreased cell death. These results suggest that zinc dyshomeostasis, along with oxidative stress contribute to the unfolded protein response during myocardial H/R and that zinc replenishment corrects zinc homeostasis, alleviates associated stress and improves cardiomyocyte survival.

Autophagy Activation Is Involved in Acidic Fibroblast Growth Factor Ameliorating Parkinson's Disease via Regulating Tribbles Homologue 3

Parkinson's disease (PD) is a degenerative disorder of the central nervous system, resulting in loss of dopamine neurons. Excessive endoplasmic reticulum (ER) stress and autophagy dysfunction play a crucial role on Parkinson's disease (PD) development. It has been showed that acidic fibroblast growth factor (aFGF) alleviates the development of PD by inhibiting ER stress. But the role of autophagy and its relationship with ER stress during aFGF treatment for PD has not been elucidated. We found that both aFGF and rapamycin (Rapa) improved 6-Hydroxy Dopamine (6-OHDA)-induced PD development as shown with histomorphology results in striatum and substantia nigra (SNpc). Additionally, aFGF promoted autophagy with increasing mTOR and decreasing p62 expressions, and then exerts its neuroprotective role in 6-OHDA-treated PC12 cells, which were abolished by chloroquine (CQ) treatment. Moreover, 4-phenylbutyric acid (4-PBA) administration inhibited the expressions of autophagy markers during 6-OHDA-treated PC12 cells, which was similar with aFGF treating PC12 cells under 6-OHDA condition. Furthermore, we had detected the expressions of CHOP and its downstream factor, tribbles homologue 3 (TRB3), a pro-apoptotic protein. We found that TRB3 and CHOP expressions were significantly downregulated after treating with aFGF and 4-PBA in 6-OHDA-treated PC12 cells and PD model. Taken together, this study has demonstrated that aFGF treatment ameliorates 6-OHDA-induced elevated ER stress and subsequently suppression of autophagy via inhibiting TRB3 activation, and consequently ameliorates 6-OHDA-induced neurotoxicity.

Hyperglycemia aggravates spinal cord injury through endoplasmic reticulum stress mediated neuronal apoptosis, gliosis and activation

BACKGROUND

Hyperglycemia has been shown to influence prognostic outcome of spinal cord injury (SCI). However, the corresponding mechanism is not very clear.

AIM

This study is expected to explore the role of endoplasmic reticulum (ER) stress in hyperglycemia aggravated SCI.

METHODS

Hyperglycemia was established in rats by intraperitoneal (i.p.) injection of streptozotocin. SCI was performed at the T10 of spinal cord through weight dropping. ER stress was suppressed by oral gavage of 4-PBA. ER stress, histological change of the injured spinal cords, neuronal apoptosis, demyelination, glial proliferation, inflammatory factor production, blood-spinal cord barrier (BSCB) permeability, TJ (Occludin, Claudin5) and AJ (β-catenin, P120) protein degradation, and locomotor recovery were determined using western blotting, immunohistochemistry, HE staining, Evan's Blue assay, BBB scores and inclined plane test, respectively. In vitro, rat spinal cord neurons cells (RSCNCs) and cerebral microvascular endothelial cells (RCMECs) were stimulated with high glucose (HG) and/or thapsigargin (TG). The effects of HG and/or TG on RSCNCs apoptosis, and AJ and TJ expression by RCMECs were evaluated with flow cytometry and western blotting, respectively.

RESULTS

Hyperglycemic rats exhibited enhanced ER stress, increased neuronal apoptosis, aggravated demyelination, increased glial proliferation and inflammatory factors secretion, more serious BSCB disruption and disturbed locomotor recovery. ER stress inhibition alleviated hyperglycemia induced adverse effect on neuronal apoptosis and BSCB permeability, whereas showed little influence on glial activation and inflammation.

CONCLUSION

ER stress was aggravated in hyperglycemic rats after SCI, and subsequently promoted neuronal apoptosis and BSCB disruption in rats.

Sodium 4-phenylbutyrate treatment protects against renal injury in NZBWF1 mice

Systemic lupus erythematosus (SLE) is an autoimmune disease predominantly affecting women and often leading to lupus nephritis and kidney damage. Endoplasmic reticulum (ER) stress has been implicated in several forms of kidney disease, but whether ER stress contributes to renal injury in SLE is unknown. To investigate this, a small molecule chaperone, sodium 4-phenylbutyrate (4-PBA), was administered to the New Zealand Black x New Zealand White F₁ hybrid (NZBWF1) mouse model of SLE. In a prevention study, treatment with 4-PBA from 20 weeks of age (prior to the development of renal injury) delayed the onset of albuminuria and significantly reduced additional indices of renal injury compared with vehicle-treated NZBWF1 mice at 36 weeks of age, including collagen deposition, tubular casts, renal cell apoptosis, and blood urea nitrogen (BUN) concentration. To test whether ER stress contributes to the progression of renal injury once albuminuria has developed, mice were monitored for the onset of albuminuria (3+ or ≥300 mg/dl by dipstick measurement of 24-h urine sample) and once established, were either killed (onset group), or underwent 4-PBA or vehicle treatment for 4 weeks. Treatment with 4-PBA blocked the worsening of glomerular injury, reduced the number of dilated or cast-filled tubules, and reduced the number of apoptotic cells compared with vehicle-treated mice. BUN and left ventricle to bodyweight ratio (LV:BW) were also reduced by 4-PBA treatment. Renal expression of the endogenous chaperones, protein disulphide isomerase (PDI), and 78 kDa glucose-regulated protein (GRP78, also known as binding Ig protein (BiP)), were increased in 4-PBA-treated mice. Together, these results suggest a therapeutic potential for agents like 4-PBA in combating renal injury in SLE.

Hydrogen Sulfide Ameliorates Blood-Spinal Cord Barrier Disruption and Improves Functional Recovery by Inhibiting Endoplasmic Reticulum Stress-Dependent Autophagy

Spinal cord injury (SCI) induces the disruption of blood-spinal cord barrier (BSCB), which elicits neurological deficits by triggering secondary injuries. Hydrogen sulfide (H₂S) is a gaseous mediator that has been reported to have neuroprotective effect in the central nervous system. However, the relationship between H₂S and BSCB disruption during SCI remains unknown. Therefore, it is interesting to evaluate whether the administration of NaHS, a H₂S donor, can protect BSCB integrity against SCI and investigate the potential mechanisms underlying it. In present study, we found that SCI markedly activated endoplasmic reticulum (ER) stress and autophagy in a rat model of complete crushing injury to the spinal cord at T9 level. NaHS treatment prevented the loss of tight junction (TJ) and adherens junction (AJ) proteins both in vivo and in vitro. However, the protective effect of NaHS on BSCB restoration was significantly reduced by an ER stress activator (tunicamycin, TM) and an autophagy activator (rapamycin, Rapa). Moreover, SCI-induced autophagy was remarkably blocked by the ER stress inhibitor (4-phenylbutyric acid, 4-PBA). But the autophagy inhibitor (3-Methyladenine, 3-MA) only inhibited autophagy without obvious effects on ER stress. Finally, we had revealed that NaHS significantly alleviated BSCB permeability and improved functional recovery after SCI, and these effects were markedly reversed by TM and Rapa. In conclusion, our present study has demonstrated that NaHS treatment is beneficial for SCI recovery, indicating that H₂S treatment is a potential therapeutic strategy for promoting SCI recovery.

Inhibition of Endoplasmic Reticulum Stress Preserves the Integrity of Blood-Spinal Cord Barrier in Diabetic Rats Subjected to Spinal Cord Injury

The blood-spinal cord barrier (BSCB) plays significance roles in recovery following spinal cord injury (SCI), and diabetes mellitus (DM) impairs endothelial cell function and integrity of BSCS. Endoplasmic reticulum (ER) stress occurs in the early stages of SCI and affects prognosis and cell survival. However, the relationship between ER stress and the integrity of BSCB in diabetic rats after SCI remains unclear. Here we observed that diabetic rats showed increased extravasation of Evans Blue (EB) dye, and loss of endothelial cells and pericytes 1 day after SCI compared to non-diabetic rats. Diabetes was also shown to induce activation of ER stress. Similar effects were observed in human brain microvascular endothelial cells. 4-phenylbutyric acid (4-PBA), an ER stress inhibitor lowered the adverse effect of diabetes on SCI, reduced EB dye extravasation, and limited the loss of endothelial cells and pericytes. Moreover, 4-PBA treatment partially reversed the degradation of tight junction and adherens junction both in vivo and in vitro. In conclusion, diabetes exacerbates the disruption of BSCB after SCI via inducing ER stress, and inhibition of ER stress by 4-PBA may play a beneficial role on the integrity of BSCB in diabetic SCI rats, leading to improved prognosis.

Dl-3-n-butylphthalide improves functional recovery in rats with spinal cord injury by inhibiting endoplasmic reticulum stress-induced apoptosis

Endoplasmic reticulum (ER) stress-induced apoptosis occurs in the spinal cord following traumatic spinal cord injury (SCI). Dl-3-n-butylphthalide (NBP) exerts an neuroprotective effects against both ischemic brain injury and neurodegenerative diseases; however, the relationship between ER stress-induced apoptosis and the therapeutic effect of NBP in SCI remains unclear. In this study, moderate spinal cord injuries were induced in Sprague-Dawley (SD) rats with a vascular clip. NBP was administered by oral (80 mg/kg/d) gavage 2 h before injury and then once daily for 28 d thereafter. Neurological recovery was assessed using the Basso, Beattie, and Bresnahan (BBB) locomotion rating scale, the inclined plane test, and the footprint analysis. Neuronal cell death was examined by TUNEL staining at 7 days post-injury. ER stress and apoptosis-related proteins were quantified by immunofluorescence staining and western blotting both in vivo and in vitro. Our results showed that NBP significantly decreased spinal cord lesion cavity area and improved locomotor recovery in SD rats after SCI. NBP also decreased neuronal apoptosis and inhibited activation of the caspase 3 cascade. Upregulation of ER stress-related proteins, such as GRP78, ATF-6, ATF-4, PDI, XBP-1, and CHOP, was reversed by NBP treatment in SD rats with SCI. Similarly, NBP effectively ameliorated ER stress and apoptosis-related protein expression induced by incubation with thapsigargin (TG) in PC12 cells. Our findings demonstrate that NBP treatment alleviates secondary SCI by inhibiting ER stress-induced apoptosis, thereby promoting neurological and locomoter functional recovery.

Chemical Chaperone 4-Phenylbutyric Acid Reduces Cardiac Ischemia/Reperfusion Injury by Alleviating Endoplasmic Reticulum Stress and Oxidative Stress

Background

Cardiovascular diseases are the leading cause of death in many countries and myocardial ischemia-reperfusion (I/R) injury is the cause of many serious heart diseases. Recent reports suggested that endoplasmic reticulum (ER) stress is associated with the progress of ischemia/reperfusion (I/R) injury. In a previous study, we illustrated that 4-phenylbutyric acid (4-PBA) reduces I/R-induced cell death in vitro through inhibiting the ER stress-initiated cell apoptosis. In the present study we investigated whether 4-PBA improves heart function in isolated rat hearts subjected to I/R and elucidated the potential mechanisms involved in 4-PBA-induced cardioprotective effects.

Material/Methods

The isolated rat hearts were subjected to global ischemia and reperfusion in the absence or presence of 4-PBA. Hemodynamic parameters (LVSP, LVEDP, ±dP/dt_max, and HR) were monitored and histopathological examination was applied. The biomarkers related to oxidative stress were detected by LDH, ROS, MDA, CK, SOD, and GSH-Px kits. A TUNEL apoptosis assay kit was used to detect apoptosis. The expression levels of ER stress and apoptosis proteins were evaluated by Western blotting.

Results

We found that 4-PBA (5 mM, 10 mM) pretreatment significantly attenuated cardiac dysfunction and depressed oxidative stress induced by I/R. Moreover, I/R activated the ER stress proteins Grp78 and PERK, which are all decreased by 4-PBA. 4-PBA pretreatment also inhibited the expression of CHOP, Caspase-12, and Bax, reduced the phosphorylation of JNK, and enhanced the expression of anti-apoptotic protein Bcl-2.

Conclusions

We elucidated the significant protective effects of 4-PBA against I/R injuries by inhibition of ER stress, oxidative stress, and their associated apoptosis.

Phenylbutyrate prevents disruption of blood-spinal cord barrier by inhibiting endoplasmic reticulum stress after spinal cord injury

This study aims to investigate the role of endocytoplasmic reticulum (ER) stress induced by spinal cord injury (SCI) in blood-spinal cord barrier (BSCB) disruption and the effect of phenylbutyrate (PBA) on BSCB disruption after SCI. After a moderate contusion injury at the T9 level of spinal cord with a vascular clip, PBA was immediately administered into injured rat via intraperitoneal injection (100 mg/kg) and then further treated once a day for 2 weeks for behavior test. Spinal cord was collected at 1 day post-injury for evaluation of the effects of ER stress and PBA on BSCB disruption after SCI. PBA significantly attenuated BSCB permeability and degradation of tight junction molecules such as P120, β-catenin, Occludin and Claudin5 at 1 day after injury and improved functional recovery in the rat model of trauma. The BSCB protective effect of PBA is related to the inhibition of ER stress induced by SCI. In addition, PBA significantly inhibited the increase of ER stress markers and prevents loss of tight junction and adherens junction proteins in TG-treated human brain microvascular endothelial cells (HBMEC). Taken together, our data demonstrate that therapeutic strategies targeting ER stress may be suitable for the therapy of preserving BSCB integrity after SCI. PBA may be a new candidate as a therapeutic agent for protecting SCI by a compromised BSCB.

Chemical chaperone 4-phenylbutyric acid protects H9c2 cardiomyocytes from ischemia/reperfusion injury by attenuating endoplasmic reticulum stress-induced apoptosis

Myocardial ischemia/reperfusion (I/R) is a potential contributor to high rates of mortality in several cardiovascular diseases. I/R initiates the unfolded protein response and endoplasmic reticulum (ER) stress, which may lead to apoptotic pathways and exaggerate I/R injury. 4‑phenylbutyric acid (4‑PBA), a low molecular weight, terminal aromatic substituted fatty acid, has been reported to function as an ER chaperone. The aim of the present study was to investigate whether 4‑PBA is able to reduce ER stress‑induced apoptosis and prevent cardiomyocyte damage during the process of I/R in vitro. Accordingly, the rat cardiomyocyte line, H9c2, was treated with hypoxia/reoxygenation as an I/R model in vitro. Myocardium apoptosis was determined with TUNEL staining. The expression of ER stress‑related proteins were examined by western blotting. The resulting data showed that I/R activates the ER stress proteins, glucose‑regulated protein 78, activating transcription factor 6 and protein kinase RNA‑like endoplasmic reticulum kinase, which were all reduced by pretreatment with 4‑PBA. In addition, pretreatment with 4‑PBA significantly inhibited the expression levels of pro‑apoptotic proteins, C/EBP homologous protein, B cell lymphoma (Bcl‑2)‑associated X protein and phosphorylated c‑Jun N‑terminal kinase, and enhanced the expression of the anti‑apoptotic protein Bcl‑2 (n=3; P<0.05). The data demonstrated that I/R initiates ER stress‑associated apoptotic pathways, and 4‑PBA pretreatment protected the cardiomyocytes from I/R‑induced cell death. To the best of our knowledge, the present study is the first to report on the cell repair mechanism of 4‑PBA against I/R damage in cardiomyocytes based on ER stress‑associated apoptotic pathways.

p53 as a retrovirus-induced oxidative stress modulator

Infection of astrocytes by the neuropathogenic mutant of Moloney murine leukemia virus, ts1, exhibits increased levels of reactive oxygen species (ROS) and signs of oxidative stress compared with uninfected astrocytes. Previously, we have demonstrated that ts1 infection caused two separate events of ROS upregulation. The first upregulation occurs during early viral establishment in host cells and the second during the virus-mediated apoptotic process. In this study, we show that virus-mediated ROS upregulation activates the protein kinase, ataxia telangiectasia mutated, which in turn phosphorylates serine 15 on p53. This activation of p53 however, is unlikely associated with ts1-induced cell death. Rather p53 appears to be involved in suppressing intracellular ROS levels in astrocytes under oxidative stress. The activated p53 appears to delay retroviral gene expression by suppressing NADPH oxidase, a superoxide-producing enzyme. These results suggest that p53 plays a role as a retrovirus-mediated oxidative stress modulator.

ROS upregulation during the early phase of retroviral infection plays an important role in viral establishment in the host cell

Recent studies suggest that low levels of reactive oxygen species (ROS) often modulate normal intracellular signalling pathways, determine cell fates and control cell proliferation. We found that infection of astrocytes with the neuropathogenic retrovirus ts1, a mutant of Moloney murine leukemia retrovirus, upregulated ROS at low levels during the early phase of infection. This upregulation of intracellular ROS with downregulation of NADPH levels during the early phase of ts1 infection was a separate event from the upregulation of ROS during the late phase while ts1-mediated cell death occurred. The treatment of apocynin, a potential inhibitor of NADPH oxidase (NOX), inhibited establishment of the ts1 virus in the host cell. These results suggested that ROS generated as a consequence of the activation of NOX may play an important role in the early events of the virus life cycle leading to the establishment of the virus in the host cell. The in vitro results were further supported by an in vivo experiment which showed that the treatment of apocynin decreased viral titre in the ts1-infected mouse brain and increased the lifespan of infected mice. This study provides the first in vitro and in vivo evidence on a mechanism for how ROS are involved in ts1 retrovirus infection and ts1-mediated neurodegenerative disease. Our findings focusing on the early phase of the ts1 retrovirus life cycle could provide a better understanding of retroviral life cycle, which may offer specific therapeutic targets for suppressing viral replication and alleviating neurodegenerative symptoms in a mouse model.

Unique N-linked glycosylation of CasBrE Env influences its stability, processing, and viral infectivity but not its neurotoxicity

The envelope protein (Env) from the CasBrE murine leukemia virus (MLV) can cause acute spongiform neurodegeneration analogous to that induced by prions. Upon central nervous system (CNS) infection, Env is expressed as multiple isoforms owing to differential asparagine (N)-linked glycosylation. Because N-glycosylation can affect protein folding, stability, and quality control, we explored whether unique CasBrE Env glycosylation features could influence neurovirulence. CasBrE Env possesses 6/8 consensus MLV glycosylation sites (gs) but is missing gs3 and gs5 and contains a putative site (gs*). Twenty-nine mutants were generated by modifying these three sites, individually or in combination, to mimic the amino acid sequence in the nonneurovirulent Friend 57 MLV. Three basic viral phenotypes were observed: replication defective (dead; titer < 1 focus-forming unit [FFU]/ml), replication compromised (RC) (titer = 10(2) to 10(5) FFU/ml); and wild-type-like (WTL) (titer > 10(5) FFU/ml). Env protein was undetectable in dead mutants, while RC and WTL mutants showed variations in Env expression, processing, virus incorporation, virus entry, and virus spread. The newly introduced gs3 and gs5 sites were glycosylated, whereas gs* was not. Six WTL mutants tested in mice showed no clear attenuation in disease onset or severity versus controls. Furthermore, three RC viruses tested by neural stem cell (NSC)-mediated brainstem dissemination also induced acute spongiosis. Thus, while unique N-glycosylation affected structural features of Env involved in protein stability, proteolytic processing, and virus assembly and entry, these changes had minimal impact on CasBrE Env neurotoxicity. These findings suggest that the Env protein domains responsible for spongiogenesis represent highly stable elements upon which the more variable viral functional domains have evolved.

Protein disulfide isomerase in redox cell signaling and homeostasis

Thiol proteins may potentially act as redox signaling adaptor proteins, adjusting reactive oxygen species intermediates to specific signals and redox signals to cell homeostasis. In this review, we discuss redox effects of protein disulfide isomerase (PDI), a thioredoxin superfamily oxidoreductase from the endoplasmic reticulum (ER). Abundantly expressed PDI displays ubiquity, interactions with redox and nonredox proteins, versatile effects, and several posttranslational modifications. The PDI family contains >20 members with at least some apparent complementary actions. PDI has oxidoreductase, isomerase, and chaperone effects, the last not directly dependent on its thiols. PDI is a converging hub for pathways of disulfide bond introduction into ER-processed proteins, via hydrogen peroxide-generating mechanisms involving the oxidase Ero1α, as well as hydrogen peroxide-consuming reactions involving peroxiredoxin IV and the novel peroxidases Gpx7/8. PDI is a candidate pathway for coupling ER stress to oxidant generation. Emerging information suggests a convergence between PDI and Nox family NADPH oxidases. PDI silencing prevents Nox responses to angiotensin II and inhibits Akt phosphorylation in vascular cells and parasite phagocytosis in macrophages. PDI overexpression spontaneously enhances Nox activation and expression. In neutrophils, PDI redox-dependently associates with p47phox and supports the respiratory burst. At the cell surface, PDI exerts transnitrosation, thiol reductase, and apparent isomerase activities toward targets including adhesion and matrix proteins and proteases. Such effects mediate redox-dependent adhesion, coagulation/thrombosis, immune functions, and virus internalization. The route of PDI externalization remains elusive. Such multiple redox effects of PDI may contribute to its conspicuous expression and functional role in disease, rendering PDI family members putative redox cell signaling adaptors.

Endoplasmic reticulum stress and lipid metabolism: mechanisms and therapeutic potential

The endoplasmic reticulum (ER) plays a crucial role in protein folding, assembly, and secretion. Disruption of ER homeostasis may lead to accumulation of misfolded or unfolded proteins in the ER lumen, a condition referred to as ER stress. In response to ER stress, a signal transduction pathway known as the unfolded protein response (UPR) is activated. UPR activation allows the cell to cope with an increased protein-folding demand on the ER. Recent studies have shown that ER stress/UPR activation plays a critical role in lipid metabolism and homeostasis. ER-stress-dependent dysregulation of lipid metabolism may lead to dyslipidemia, insulin resistance, cardiovascular disease, type 2 diabetes, and obesity. In this paper, we examine recent findings illustrating the important role ER stress/UPR signalling pathways play in regulation of lipid metabolism, and how they may lead to dysregulation of lipid homeostasis.